Plastic container with rounded shoulders

ABSTRACT

A plastic container for the storage and transport of liquids, particularly aggressive liquids, comprising a practically rectangular bottom, a top wall with a filling or pouring hole, and standing walls which each connect to the circumferential seam of both the bottom and the top, and four standing edge strips each connecting two walls, which container is manufactured by the blow-molding process, wherein the standing wall portions have a convex form, wherein either the standing edge strips widen at the top and the bottom and, as seen in a cross-section running parallel to the bottom, the standing edge strips have a radius of curvature equal to or greater than that of the standing wall portions to which they are connected.

CROSS REFERENCE TO RELATED APPLICATIONS

This application was filed pursuant to 35 U.S.C. 371, based onInternational application No. PCT/EP01/07831, filed Jul. 6, 2001, andclaims priority from EPO application No. 00202462.8, filed Jul. 11,2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to plastic containers for the storage andtransport of liquids, particularly aggressive liquids.

2. Prior Art

The above type containers comprise a practically rectangular bottom withrounded corners, a top with a filling or pouring hole, four standingwalls which each connect to the circumferential seam of both the top andthe bottom, and four standing edge strips each connecting two walls, arounded corner of the bottom and a corner of the top, which container ismanufactured by the blow molding process.

Such containers are widely used and frequently stacked with othercontainers on a pallet and transported. Consequently, such containersmust be self-bearing, meaning that they should have sufficient strengthto withstand the weight of other containers and their contents stackedon top of them during storage and transport. FR-A-26178, for instance,describes such containers.

However, the strength of such containers, particularly of containersholding 15 kg of liquid or more, is limited. Furthermore, it wasobserved that the strength of containers holding aggressive liquids,especially liquids that (partially) migrate into the wall material, isadversely affected, often to such an extent that they cannot withstandthe usual load. The option of thicker walls, by using more material inthe blow molding process, is uneconomic. Furthermore, if the containersare to hold thermally liable liquids that show self-acceleratingdecomposition, such as organic peroxides, they cannot be made toosturdy, since such containers have to rupture at fairly low pressures toprevent hazardous situations (such as explosions) as per therecommendations of the United Nations Committee of Experts on theTransport of Dangerous Goods.

The object of the invention is to present a new type of blow-moldedcontainer with increased compression strength at equal weight that issuitable for holding said aggressive fluids. This is achieved by meansof a special container design. Of course, this design will also allowthe production of lighter containers with the same strength asconventional containers, thereby reducing the amount of plastic materialrequired.

SUMMARY OF THE INVENTION

In one embodiment the invention comprises a plastic container for thestorage and transport of liquids comprising a substantially rectangularbottom, a top with at least a filling or pouring hole, four standingwall portions which each connect to the circumferential seam of both thebottom and the top, and four standing edge strips each connecting twowall portions. The standing wall portions are convex and the standingedge strips widen at the top and the bottom and, as seen in across-section running parallel to the bottom, the standing edge stripshave a radius of curvature equal to or greater than that of the standingwall portions to which they are connected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective side view of half a container according tothe invention,

FIG. 2 shows a front view, partly in standing section, of the containerof FIG. 1,

FIG. 3 is a top view of the container of FIG. 1.

FIG. 4 is a side view, partly in cross-section, of the container of FIG.1,

FIG. 5 is a detail of the top right-hand part of the container of FIG.2,

FIG. 6 a shows cross-section C–C′ of FIG. 1,

FIG. 6 b shows cross-section D–D′ of FIG. 1, and

FIG. 7 is a bottom view of the container of FIG. 1.

The same reference numerals are used in the figures for the samecomponents.

DETAILED DESCRIPTION OF THE INVENTION

The plastic container according to the invention stands out because thestanding edge strips widen at the top and the bottom, such that theaverage length of the bounding line between the top and bottom surfacesand the wall portion is 0.15 to 3 times the length of the bounding linebetween the edge strip and the top and bottom surfaces. Because the edgestrips widen toward the top and also toward the bottom, the delicatetransition in the corners of the container is made smoother, resultingin improved transfer of the vertical forces.

In a container according to another embodiment of the invention, theedge strips take on a flatter form, i.e. as seen in a cross-sectionrunning parallel to the bottom, the standing strip has a radius ofcurvature equal to or greater than that of the connecting wall portion,in which process the above-stated force transfer is improved. A sharpedge between standing strip and wall element is undesired because itreduces the ability to pass a drop test of a filled container. Thereforeit is preferred that the transition from the standing strip into thewall element is a smooth one.

In preferred containers the standing strips are stiffened in thelongitudinal direction, perpendicular to the plane of the bottom and topwalls, for instance by means of a conventional ridged, or otherwiseribbed, structure. In this way the force transfer is improved evenfurther and containers can be stacked with a reduced risk of collapse.

According to a feature of the invention, the width of the end portion ofthe edge strip in one embodiment is about ⅓or more of half the height ofsaid edge strip. In a vertical section, perpendicular to the plane ofthe bottom and top walls, this end portion moreover preferably has aradius of curvature which becomes increasingly smaller, so that the endportion transposes smoothly, or substantially smoothly, into the top andbottom surfaces. This means that the radius of curvature, starting fromthe bounding line of the edge strip and the top or bottom, in eitherdirection increases continuously until it matches the radius ofcurvature of edge strip and top or bottom, respectively.

In another preferred embodiment, the wall elements are at least convexin the vertical plane, meaning that none of the side walls have flatsurfaces. When stacked, the side walls of adjacent containers willtypically touch at midlength. This may be less desirable because thelabels of the adjacent containers will then rub against each other andbecause locking elements as disclosed in FR-A-26178 cannot be locatednear the top and bottom walls.

However, the strength of containers with such convex walls was found tobe unsurpassed. Especially stacked containers that are stored in theusual way, meaning that the temperature is not perfectly constant, werefound to have improved stack stability. Although there is no wish to belimited to such a theory, it is expected that such preferred containerswill be better at resisting deformation, e.g. due to a vacuum created inthe container when the temperature decreases.

In a further preferred embodiment, the top wall of the container isequipped with one or more vertical elements that have, in total, two ormore slots or other connective means, which are located in a recessedarea of the top wall. The slots are not in the horizontal plane. Ahandle can be attached to the container using these slots and fasteningmeans in a conventional way. Preferably, the recessed area of the topwall, the handle, fastening means, slots, and vertical elements aredesigned such that the top of the handle, when in its lowest position,will not interact with the bottom of another container stacked on top ofit, while a gloved hand is able to slide between said handle and the topwall when the top of the handle is in its highest position. Such adesign increases the load bearing capacity of a container with handle,because most of the forces are carried through the sides of top andbottom elements and easily transferred to the wall and the standing edgestrip elements, while maximizing the volume of the container andallowing easy handling, such as emptying, of said container.

Preferably, the handle is not a (hollow) integral part of the topportion of the container, such as is typically seen in conventional(smaller) containers such as milk jugs. Such (hollow) handles make theblow molding operation according to which the present containers aremade much more cumbersome and typically result in a less than optimaluse of the plastic material employed. More specifically, in order toprevent weak spots around the handle area, a thicker wall is typicallyneeded in comparison to containers with the same strength but withoutsaid (hollow) handles. It is furthermore noted that integral handles areoften designed such that they protrude from the top wall. In that casethe chances of passing the drop test of a filled container is reducedwhile also stacking is less efficient.

A container according to the present invention is pre-eminently suitedto being made in a mold, which as is usual consists of two half-molds inmirror image relationship to the plane of symmetry of an upright centralplane of the container. These half-molds can be opened up and closedtogether again, enabling a process in which a premold is laid up againstthe inner wall of the mold by means of blow molding, where the containercan be released after curing. Such a mold is normally limited to aspecified volume, for instance 15 liters. There are conventional moldswherein one or more extra segments are introduced such that the wallsection of the containers is extended and, accordingly, the volume ofthe final containers is increased, for instance to 30 or 60 liters. Theintroduction of such additional segments causes a disruption in the wallelements of the container, unless the sides of the containers are flat.For convex wall elements according to the invention, however, thedisruption in the walls (meaning that the radius of the wall, whenviewed in the plane perpendicular to the wall and perpendicular to thebottom, does not change continuously over the full height of thecontainer but shows distinct transitions between parts with a differentradius) causes the containers to be less strong.

The invention therefore has for its object to provide the half-mold withan interchangeable middle portion which serves to restrict the size ofthe convex middle section of the wall and the part of the edge striplocated between its end portions, which interchangeable middle portionsdiffer in height and have distinctive radii of curvature so as to give asmooth curve of the middle sections and the end portions of the totalside wall.

The container according to the present invention consists of asubstantially rectangular bottom part 1 with rounded corners, a top wall2, and standing wall portions 3, 4 that connect the top and bottomwalls.

The wall portions consist of side faces 3, 4, with sandwiched betweenthem an edge strip 5 which connects these faces. Preferably, the sidewalls are convex in the vertical plane, as shown in FIG. 2. Morepreferably, the bulging of the container is such that the circumferenceat half height of the container is at least 5%, preferably at least 10%more than the circumference of the side walls at a distance of 1 cm fromthe top and/or bottom. Preferably, the circumference at half height ofthe container is not more than 50%, preferably not more than 30% morethan the circumference at the top and/or bottom of the container.

According to the main feature of the invention, the edge strip 5 widenstoward the top into part 6 and toward the bottom into part 7.

This widening into 7 is likewise such that the length of the averagebounding lines 8 and 8′ between the side faces 3, 4 and the bottom ismore than 0.15, preferably more than 0.3, most preferably more than 0.6the length of the average bounding line 9 between the widened edgestrips and the bottom. At the same time, the length of the averagebounding lines 8 between the side face 3 and the bottom is less than 2,preferably less than 1, more preferably less than 0.8, and mostpreferably less than 0.75 the length of the average bounding line 9between the widened edge strips 5 and the bottom (see FIG. 7). The sameholds, mutatis mutandis, for the widening of the edge strips 5 into 6and the bounding line of edge strips 5 and walls 3 with the top surface,such that the rounding at the top is similar to the rounding asdescribed for the bottom. This means that the edge strip 5 runs smoothlyin the shape of a shoulder into the bottom and top. The rounding isdescribed for the connection with the bottom since there the boundinglines are not complicated by the opening(s) as present in the top.

The top surface 2 preferably is sectioned and may comprise a U-shapedhigher portion 11 sandwiching a lower portion 10 which has the fillingor pouring hole 12. The U-shaped portion preferably is capable ofinteracting with a recession in the bottom wall of another container inorder to increase the stability of containers stacked on top of oneanother. The lower portion 10 can also have fixing elements 13,preferably slotted, for mounting a handle. Further, a vent 14 can befitted in the top surface, which members, however, fall outside thescope of the invention. The bearing area of the top wall is formed bythe U-shaped portion 11, optionally together with the handle, whichtherefore takes up the forces of the containers stacked thereon. Theseforces can be transferred via the shoulder part 6 to the standing wallstrip 5 and via the shoulder part 7 to the bottom.

It was observed that in a preferred embodiment, the ribbed structure ofthe edge strips is such that essentially the whole of the edge strip 5,including the shoulder parts 6 and 7, is ribbed. More preferably, atleast one rib ends less than 40 mm, preferably less than 20 mm, morepreferably less than 15 mm, and most preferably less than 12.5 mm awayfrom the plane of the top wall 2. In FIG. 5, a container is shown wherethree recessed ribs end at a distance of 11.4 mm from the plane of thetop wall.

FIGS. 6 a and 6 b show cross-sections of the connection between thebottom wall and the edge strip 5 and the side wall 3, respectively. Theypresent an example of how the edge strips and the side walls aresmoothly connected to the bottom wall. For a container with a size of15–60 liters, a suitable radius for the transition of side walls and/oredge strips into top wall and/or bottom wall was found to be greaterthan 5 mm, preferably greater than 8 mm, and less than 100 mm,preferably less than 50 mm, more preferably less than 30, and mostpreferably less than 20 mm, such that a smooth rounding is obtained.

If so desired, all walls may be equipped with (further) conventionalelements that interlock with elements of adjacent containers to furtherincrease the stability of stacked containers, i.e. elements that preventthe shifting of containers so that the stability of the stackedcontainers is increased. Also, the containers may optionally containconventional elements on the side walls and/or edge strips to fix a(sleeve) label.

The material used in the blow molding process to form the containersaccording to the invention can be any suitable conventional material.Typically, use is made of a polyolefin resin. Optionally, use is made ofa polyolefin copolymer or modified polyolefin, such as grafted and/orbranched polyolefin (co)polymers.

It is noted that the edge strips 5 in the top view of FIG. 3 preferablyare visibly flatter than the side walls, i.e. they have a larger radiusof curvature. This increases the strength of the container.

It is noted that the length a of the upper and lower end portions 6, 7of the standing wall strips 5 preferably is about ⅓ the half-height h ofthe edge strip 5, see FIG. 2. The dividing line A—A and the dividingline B—B located underneath it can also indicate the jointing face ofinterchangeable half-molds in the blow-molding process.

It has been established by computer calculations that an averagetransfer force of 4,800 N can be achieved with blow-molded conventionalcontainers of 25 liters, with a weight of 1600 g., made fromhigh-density polyethylene. With the smooth shoulders 6, 7 as proposed bythe invention, a force of 7,000 N can be achieved while retaining thesame wall thickness, i.e. while using the same quantity of materialnecessary for the manufacture of the container.

Preferably, the edge strips 5 are strengthened even further by means oflongitudinal stiffening parts 15, as shown in FIGS. 2–4, which can beachieved by a ridged cross-section. In such a case the transfer forcescan even reach 8,300 N. In a production run containers were produced inaccordance with this most preferred embodiment. The containers had anaverage weight of 1450 g. The average strength was not 8,300 N but 7,000N. Clearly, the present invention allows stronger container to beproduced using conventional techniques that have a higher strength atlower weight.

The blow-moulding process is deemed to be known to the skilled personand requires no further elucidation. The molds are assembled fromcomponents known per se, although according to the invention, thespecial feature of the proposed mold is that the intermediate portionforming the boundary for the middle section between the separating linesA—A and B—B is interchangeable. Owing to this exchangeability option,the mold can easily be increased or decreased in size depending on thedesired volume of the container. The interchangeable middle part of themolds take a form such that the curve of the radius of curvature of theend portions toward the middle section is smooth and continuous in allsituations.

The invention is not limited to the above-described embodiment.

1. A plastic container for the storage and transport of liquidscomprising a substantially rectangular bottom, a top with at least afilling or pouring hole, four standing wall portions which each connectto the circumferential seam of both the bottom and the top, and fourstanding edge strips each connecting two wall portions, wherein thestanding wall portions are convex and wherein the standing edge stripswiden at the top and the bottom and, as seen in a cross-section runningparallel to the bottom, the standing edge strips have a radius ofcurvature equal to or greater than that of the standing wall portions towhich they are connected.
 2. A container as claimed in claim 1 wherein,as seen in vertical cross-section, the radius of curvature of thewidening end portion of the edge strip at the top and the bottom becomesincreasingly smaller, so that this end portion transposes substantiallysmoothly into the top and bottom surfaces.
 3. A container as claimed inclaim 1 wherein one or more of the standing strips are stiffened in thelongitudinal direction.
 4. A container as claimed in claim 3 wherein thestiffening is attained by means of a ribbed structure giving a ridgedcross-section to the strip.
 5. A container as claimed in claim 1 whereinthe end portion of the edge strip is about ⅓ of half its height.
 6. Acontainer for storage and transport of liquids comprising asubstantially rectangular bottom, a top with a filling or pouring hole,four standing wall portions each connecting to the circumferential seamof both the bottom and the top, and four standing edge strips eachconnecting two standing wall portions, which container is manufacturedby a blow-molding process, wherein the standing wall portions are convexand wherein, as seen in a cross-section running parallel to the bottom,the standing edge strips have a radius of curvature equal to or greaterthan that of the standing wall portions to which they are connected. 7.A container as claimed in claim 6 wherein one or more of the standingstrips are stiffened in the longitudinal direction.
 8. A container asclaimed in claim 6 wherein the end portion of the edge strip is about ⅓of half its height.